Recognised as Chemical element
Helium
- He
- Z = 2
- noble gas
Helium (He) is element 2, a noble gas in period 1 and group 18. Its standard atomic weight is 4.0026 Da. Weights follow IUPAC standard atomic weights, 2021 revision.
Identity
SymbolHe
Standard atomic weight4.0026atomic mass units (Da)
Mass in kilograms6.6464737 × 10^-27
Categorynoble gas
Group18
Period1
Blockp-block
Electrons in a neutral atom2
Neutrons in the most common isotope2≈
Quantities
Molar mass4.0026 g/mol
Mass of one mole4.0026 grams
Atoms in one gram1.5045572 × 10^23
Mass of one atom6.6464737 × 10^-24 g
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